This invention relates to an information display device, comprising:
input means for receiving bursts of information units, PA1 presentation means comprising a display area for displaying said information units, said presentation means being adapted for scrolling the information units through the display area at a specific scroll speed, PA1 control signal generator means for generating a control signal, said control signal generator means comprising evaluation means that are adapted for generating an evaluation signal representative of an average rate at which said information units are received at said input means, said control signal being derived from said evaluation signal, and in that said presentation means are adapted for controlling the scroll speed in response to said control signal. The present invention is based on the following insight: When information units are received separately at more or less regular intervals, each information unit can immediately be scrolled into the display area. Thus, the scrolling can be controlled directly by the reception of individual information units. In many information transfer systems, however, a whole message, comprising a plurality of information units, is conveyed in a very short time, for instance in a data packet. Various types of data packets may be conveyed, some comprising information units that are to be presented on the display, while others convey other information, like for instance data that is (currently) not relevant for the display device. The receiving apparatus usually comprises a decoding device that decodes these data packets (insofar necessary), filters out non-relevant data and passes to the display device only those information units that are currently to be presented. Thus, information units are received by the display device in short bursts at a high momentary reception rate. In such a system, it would be most disadvantageous if the scrolling were controlled directly by the reception of individual information units; the message conveyed in the data packet would scroll into the display area at high speed and, if the length of the message exceeds the display capacity, the beginning of the message would scroll out almost immediately. Only the end of the message would remain visible in the display for some time, until a next message is received. Consequently, a lower scroll speed is desirable so that the beginning of the message can also be read comfortably. To this end, a FIFO-type (First In, First Out) of buffer can be applied which is filled with the information units at the high momentary rate at which these are received and which emits the information units at a much lower (predetermined) rate, corresponding to a comfortable scroll speed. There may, however, be large variations in what individual users find as a comfortable scroll speed; some users can absorb information at quite a high speed while others need much more time. To satisfy almost all users, the scroll speed must be rather low. Then, it may happen that a new message is received when the previous message is still scrolling through the display and part of it has not yet been shown. In this situation, either the new message must be stored for later presentation, thereby losing its exact timing and risking the loss of the message due to limited storage capacity in the buffer, or the presentation of the previous message must be aborted, leaving part of that message unseen. Both solutions are objectionable. The present invention discloses another solution, that is particularly advantageous when the messages have a strong real-time character, like for instance the text lines of a song text that should be presented coinciding with the lines being sung. According to the present invention, the scroll speed is controlled in response to a control signal that is derived from the average rate at which information units are received by the display device. Thus, the scroll speed is low when, for instance, a slow ballad is played, and high when, for instance, a fast rap-song is played. PA1 if the average rate of reception is lower than the scroll speed, the control signal must follow slowly, i.e. a low-pass characteristic. If the modification factor .alpha. is set to a very small value, i.e. close to zero, a decrease in the average rate of reception is followed very slowly, which is advantageous if the scroll speed was already not too high for reading. Once the scroll speed is so low that lowering it further does not improve the readability of the presented messages, or may even adversely affect the understandability of the full message, the modification factor is set to .alpha.=0. If, on the other hand, the scroll speed was high (with respect to a convenient reading speed) when the average rate of reception decreases, it is more advantageous to follow that change rapidly, i.e. by setting the modification factor .alpha. equal to 1 or a bit smaller than 1. In that way, the scroll speed is lowered as soon as possible, thereby quickly improving the readability of the presented messages. PA1 if the average rate of reception is higher than the scroll speed, the control signal must follow rapidly and preferably with an "overshoot", i.e .alpha.&gt;1, to compensate for the scroll speed being too low during the preceding period. The amount of overshoot can be optimized by taking into account how many information units of the previous message are still to be shown when a next message is received. After reacting upon an increased reception rate by producing an overshoot in the scroll speed, thus quickly reducing the lag in the presentation, the low-pass characteristic described hereinabove will make the scroll speed slowly approach the new reception rate.
Information display devices are applied in apparatuses that can, in general, be divided into two classes:
1. Apparatuses that contain all information within the apparatus itself. In these, the rate at which information is presented on the display can be under the full control of its user. An example of this is a Personal Organiser; the user can browse through the information contained in the Organiser at his own preferred speed. PA0 2. Apparatuses that rely on information which becomes available at a rate that cannot be fully controlled by the apparatus or its user. In these, the speed at which information is presented on the display is often dictated by the rate at which information is received from the source. Examples of this are a receiver for broadcast messages and a song text display coupled to a Digital Compact Cassette (DCC) player or to a Digital Audio Broadcasting (DAB) receiver.
The invention relates to an information display device for use in an apparatus of this second class. An example of a display device for presenting, e.g. song texts , is disclosed in European Patent Application 0 561 435. In this document, a solution is sought for the problem that the display area is often insufficient to present a received message in full. A conventional way of presenting a long textual message on such a small display is by scrolling the message through the display area, i.e. part of the text is shifted through the display area while successive characters (or lines of text) from the message are added at one end of the display area and preceding characters (or text lines, respectively) are removed at the other end. The speed at which a message is scrolled is usually fixed or determined by special codes contained in the message, such that an average user finds the reading speed acceptable.